American Water—a New Jersey-based water and wastewater treatment company with operations in 47 states—found a drop-off on certain days of the week. Microsoft, on the other hand, came to a different conclusion about its emails. Do you know your best times and days?

The data has allowed communicators at American Water to tell people who wish to email on low-readership days, “You’re not going to get the same level of open rates or readership or engagement that you’re seeking,” says Michael Wood, senior director for internal communications.

2. The secrets of A/B testing.

Microsoft uses this method to try out its subject lines before firing off one proven to connect with employees. You don’t have to run an exhaustive study to use A/B testing.

3. How many words your subject lines should contain.

Plus, the sheet offers examples of the types of subject lines that work best at Microsoft. No surprise: “New pub opening on campus” did well.

4. What you can learn from ‘ignore rates.’

“Open rates tell you they got it,” says Michael DesRochers, managing partner at PoliteMail, “but if you have a high ‘ignore rate,’ they’re not getting the message.”

5. Why all those links in emails drive down your readership.

Surprisingly, all those blue underlined words don’t boost engagement—quite the opposite. How many links would be ideal? The guide reveals the answer.

6. Aspects of design for mobile that you might not have considered.

Is it possible that graphical headlines are reducing your click-throughs?